Regulating system



Dec. 11, 1934. I A; p HAYWARD ET A 1,984,187

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Dec ll, 1934. A. P. HAYWARD ET AL 1,984,187

REGULATING SYSTEM Filed April 19, 1932 13 Sheets-Sheet 6 WITNESSESZ INVENTORS 7720/1705 5 FZFO9// ana frnok Pfi'ayn a d ATTORNEY Dec. 11, 1934. A. P. HAYWARD ET AL REGULATING SYSTEM Filed April 19, 1952 13 Sheets-Sheec Dec. 11, 1934. p HAYWARD ET A 1,984,187

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ATTORNEY Dec. 11, 1934. A. P. HAYWARD ET AL 1,984,137

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Dec. 11, 1934. AP. HAYWARD ET AL 1, 8 ,187

REGULATING SYSTEM Filed April 19, 1932 13 Sheets-Sheet 13 WITNESSES: 7% lNgv EgoRs. a /g I O/WOS (/fC 2 g g 0/70 firrva/oP/Vayward BY g ATTORNE calls" transferring,

' electrical power-systems,

maximum-power-system efliciency or Patented een, 1934 t h PATENT OFFICE Y issuer nEGULArmG srs'rnu Arnold P. Hayward,

Bellevue, and Thomas E.

G Purcell, Pittsburgh, Pa. Application Apr-i119, 1932,*Serlal No. 606,20

' Our invention r V lates to regulating systems and has particular relation to systems for automatiq termined schedule, the control of a load-adjusting device from one to another of a parallel-operated machines.

Our invention has particular applicability to it being capable of adother predetermined manner the distribution of electrical generating unitswhich operate in parallel to supply a variable-demand system load. r

Due to the rapid growth inthe capacity .and extensiveness of electrical power systems, features of operating economy and efilciency are assuming increasingly greater importance, and it is with such features that the system ofour invention is primarily concerned.

Present day power systems utilize a relatively large number of separate generating units which operate in parallel to supply a common load. In a large percentage of cases, this load may vary 5 over a considerable range, the power demand on many generating stations normally. being of a fluctua ing nature.

- and, in many casesfof certain other The past practice of allowing each of the several parallel-operated units to assume a pro rata share of the total load supplied as the magnitude of demand changes, prevents, particularly load-efficiency highest operating economy load is varied characteristics, the from being realized when the total throughout a substantial range.

The distribution of load among the several units which is most advantageous, for any given value oftotal output, must thus take account of the inherent efli'ciency of each of the generating units, factors. It will be evident, therefore, that increased operating economy of an electrical power system can be obtained through a proper control of load distribution among the several the system.

To be of the greatest utility, it is apparent that a system of load-distribution control should be self -operating or automatic, and susceptible of being pre-set for any loading combination among the generating units which may prove most desirable.

in accordance with a prede-.

Manufacturing Company,

generating units in mined load distribution amon ply sources are effectively rea In U. S. Patent No. 1,920,544, which issued Aug. 1, 1933 to J. H. Ashbaugh and R. A. Geiselman, and which is assigned to the Westinghouse Electric &

there is described a systhe control of to another'of units in acthe several suptem which automatically transfers device from one of electrical generating cordance with changes in the total load supplied by all oi the units- In that system, to which the term program-load control" may aptly be applied, transfer operations, which are initiated by contact closure of load-responsive means associated with the generator unit under regulator control, are caused to proceed in accordance with a predetermined program or schedule.

When applied to a power system, this programload-control equipment acts to route the load-adjusting impulses from a regulator selectively among the several generating units in the station in a manner that total load increments .are progressively taken on by individual units selected according to the predetermined program. pro may be chosen to eflect a predetermined distribution of load among the generating units which so accords with their efliciency characteristics that the operating economy-of the system is thereby raised. I

Our invention is directed to an improved form of program-load control system which possesses the features and advantages partic hereinafter. I

There have been proposed regulating systems capacity is ineffective such demands. In an alternating current power system involving a transmls ionline, for example, the stability and power limits of the line are, as a result, substantially diminished by the application of such a regulating systein to the generating units which supply the line.

It is, accordingly, a general object of our invention to provide regulating means for a plurality of electrical power sources supplying a commoh load whereby the distribution of load among the several sources may be automatically adjusted in a predetermined manner, and, at the same all of the several their normal abilsudden changes in total power trol valve prime movers.

In the case of a multi-valve steam turbine, for p may be essential that a higher rate of total load change be available. If the regulator is caused to control the units in groups, as, for example, in pairs, instead of singly, such a higher increment control of the several generating units supervised.

In certain instances, when a multi-generating unit power station is supervised by a programtroller.

An additional object of is to provide means whereby the g A further object of our invention is the provision in a program load control system of a specialcontrol or skip switch with each generatmore of the generating units.

an automatic In sideration, it is likewise desirable that some ar-.

by a suitable load-changing impulse from the regulator.

An additional object of our invention, therefore, is to provide means for interrupting the regulator control while a transfer operation is in progress.

In controlling the loading oi a power station the generating units of which are supervised by program-load-control, it is sometimes desirable to supply the load-adjusting impulses manually instead of from an automatic regulator. For such an arrangement there is a possibility that impulses in both the load-raising and load-lowering directions may simultaneously be set up, which if allowed to reach the load-adjusting devices of the generating units, would cause damage thereto.-

Accordingly, a further object of our invention is to provide means for preventing load-adjusting impulses in both directions from simultaneously erating units supervised. In order that an operator in this control room may be informed as to the valve positions of each of the turbines, a signal system involving-valve-position indicatin lights is, therefore, of utility.

A further'object of our invention, therefore, is to provide in a program load control system, a systemof indicating lights by means of which the valve positions of each of the generating units supervised may be communicated to an operator at a remote point.

In the operation of a program-load-control system applied to a steam-turbine generating unit power plant, when all of the units under supervision have been fully loaded and the regulater-control transfer equipment has reached its limit of travel in the load-demand increasing or forward direction, further load-raising impulses from the regulator may, if allowed to reach the generating unit to which the regulator is assigned,

cause the governor-calibrating motor to continue to increase the tension of the calibration-changing spring even though the completely opened position of all of the turbine valves has been reached. In practice,- it is found happens atime delay to responsiveness that when this of the governor to subsequent load-lowering impulses is introduced because tion with a regulator or switching means permit the excess tension in the adjusting spring must first be relieved by a reversing action of the motor.

A still further object of our invention, therefore, is to provide means for disconnecting the regulator from the generating units when the full capacity of all of the several units supervised by a program-loadcontrol system has been brought into action.

- In practicing our invention, the complete program-load-control system involves, in combinaequivalent load-adjusting means, for controlling the governor settings of the several turbine generating units supervised, a motor-operated selector switch for transferring regulator controlamong the generating units and for routing transfer-control circuits, a set of machine and sequence receptacles for changing the transfer operation, sequence or program, auxiliary control relays, and turbine-valve-operated switches associated with each generating unit for actuating the selector switch when a controltransfer operation is to be effected. In addition, switching devices for permitting the regulator to control the generating units in pairs instead of singly, skip switches for taking one or more of the units out of the program, valve-positionindicating lamps and other auxiliary equipment are also included in the system.

Ihe program-selecting machine and sequence receptacles above mentioned, which are shown in the system of our invention about to be described, are disclosed and claimed in a second U. S. Patent No. 1,907,517, 1933, to R. De'Camp,

which issued May 9, and which is also to Westinghouse Electric. & Manufacturing Company. As is pointed out in that patent, when combined with a program-load-control system, such the sequence of transfer operations to be changed at the will of an operator, so'that an adjustable or selective program of control transfer is thereby obtainable.

Our invention itself will best be understood through the following description of specific embodiments thereof when taken in conjunction Fig. 3 is a diagram of curves illustrating the 1 heat consumption and heat rate characteristics of a three-valve turbine of the type illustrated in Fig. 1;

Fig. 4 is a diagram showing four sets of heatconsumption curves assumed to respectively apply to the four turbine generating units shown in Fig. 1;

Fig. 5 is a diagram showing the comparative slopes of the several individual sections of the heat consumption curves of Fig. 4 for the purpose of determining the most economical program of transfer operations.

Fig. 6 is a table showing several of the different transfer-operation-sequence schedules which the program-load-control system of Figs. 1 and 2 is capable of effecting;

Fig. '1 is a representation of a typical governing system for a three-valve steam turbine utilizing oil-operated relays intermediate the fiyball governor and the'turbine valves and illustrating a preferred manner in which valve-position-actuated contacts for all of the valves may be combined into a single-transfer-initiating switch mechanism for operation by the governing syslines X-X and XI-XI, respectively,

one of the oil-relay con- Vm-Vm 01 F '1;

Fig. 12 is a diagrammatic view of the eight sets of contact members of the switch of Fig. 9 connected in the circuits shown as being associated with generating unit Am the system of Figs. 1 and 2;

- s.'13-and 14, when considered together, comprise a diagrammatic view of apparatus and circuits combined with the fundamental programload-c'ontrol system of Figs. 1 and 2 in such manner that either individual or parallel-pair control operation of the generating units supervised may be effected;

Fig. 15 is a plan view showing the mechanical construction of the motor-operated selector switch which is diagrammatically represented in Figs. 2 and 14;

Fig. 16 is a side elevation view of the switch of F18 1 Fig. 1'1 is a side elevation view, partially in section, showing the construction of a pair of receptacles and cooperating plug members of a type suitable for use bythe program-selecting switching arrangement utilized in the control transfer system shown'in Figs. 13 and 14, as well as in the system of Figs. 1 and 2;

Fig. 18 is a simplified schematic representation of that of the transfer-initiating "circuit conductors To control the flow of of a load-balancing scheme utilized by the parallel-pair control equipment of the automatic transfer system of Figs. 13 and 14;

Fig. 19 is an operation-explanation table showing the several steps or positions assumed by the transfer equipment in the program-load control systems of Figs. 1 and 2 and Figs."13 and 14; and

Fig. 20 is a diagrammatic view of one of the generating units adapted for parallel pair operation as shown in Fig. 12 with which the skip switch and valve position indicating lamps depicted in Fig. 1 are combined.

Referring to the drawings, and particularly to Figs. land 2 thereof it will be observed that the terminating at the right-hand side of Fig. 1 are continued at the left-hand side of Fig.2 in a manner that the apparatus illustrated in the two figures is interconnected. In the explanation and description which is to follow, like reference characters in the two separate figures will designate conductors which are common'to both and which continuefrom one to the other.

In Fig. 1, the four separate generating units which the program-load-control system of our invention is to supervise are designated generally by units A, B, C and D, respectively. Generating unit A comprises an alternating-current generator 20 disposed to be driven by a prime mover 21, illustrated in the form of a steam turbine. The generator is illustrated as being of the three-phase type comprising armature windings 23 and an exciting field winding 24.

Similarly, generating unit B comprises a generator 25 and a prime mover 26; unit C a generator 28 and a primemover 29; and unit D a generator 30 and a prime mover 31.

The armature windings of the several generators named are connected in the manner shown to a three-phase power circuit designated by conductors 34. 35 and 36 at the middle of the figures. The generator field windings are illustrated as being energized by direct-current derived from conductors 38 and 40. of positive and negative polarities respectively. These conductors may be supplied from any suitable direct-current energy source (not shown).

Prime movers 21, 26, 29 and 31 are each illustrated in the .form of a steam turbine of a well known multi-valve type which is now generally applied in large capacity installations. The turbines may be supplied with driving steam through conduits 42, 43, 44 and 45, respectively, from steam boilers or other suitable source (not shown) this steam in the most economical manner, a plurality of control valves are inserted in each of the conduits named.

Prime mover 2-1, for example, utilizes a primary valve 48 which supplies one set of steam jets in the turbine, a secondary valve 49 which supplies a second set of jets, and a tertiary valve 50 which supplies a third set of steam jets. In operation, both the secondary and tertiary valves remain closed until the primary valve has been completely opened, at which time the secondary valve also opens and, causes the second set of steam jets to aid the first in driving the turbine. When the secondary valve has been completely opened, the tertiary valve also opens and brings into action the third set of steam jets.

In a similar manner, prime movers 26, 29 and 31 are each provided with primary, secondary, and

'tertiary input control valves represented in the same relative positions as are the valves of prime I mover 21 already described.

'The position of the movable members of the control valves is determined by a speed-responsive governor mechanism in a well known manner. As illustrated, prime mover 21-, for example, drives through a suitable mechanical connection a flyball mechanism 55 which transmits governing movements to anarm 57 which is shown as being pivoted at its right end and connected at the other end to the control valves by means of members 59, 60 and 61, respectively. An increase in the speed of prime mover 21 acts to move lever 57 downwardly to close the valves, w lo a decrease in speed similarly acts to move the lever upwardly to open the valves and thus admit more steam.

In a similar manner, the prime movers .26, 29 and 31 are each provided with fiyball governing mechanisms which act to control the positions of the input control valves in accordance with the speed of the prime movers. Since the showing of the valve and governing mechanisms for all of the units of Fig. 1 is a duplicate, no further detailed description for units B, C and D is deemed necessary.

The showing of the governing mechanisms in Fig. 1 is greatly simplified as compared with the equivalent actual arrangement utilized by large capacity turbines, one well known form of which is illustrated in Fig. 7 and which will later be described.

Inasmuch as a direct relation exists between theinput to the driving prime mover and the out-- put of the driven generator in a generating unit of the type under consideration, changing the input of the steam turbine-will cause the generator to correspondingly change its output. It will be observed that, in the case of the particular type of governing mechanism shown, for loadings within the range of the primary valve the secondary valve is closed while for loadings above the primary range the secondaryvalve is also opened, and for loadings above the combined primary and secondary range, the tertiary valve opens. This particular relation is graphic'ally represented by the curves of Fig, 3 which will be more completely explained hereinafter.

The governing mechanism so far described is capable of maintaining the speed of the generating unit within reasonably close limits, but is not sufiiciently sensitive to eifect the accurate regulation of the generators, which, in an alternating-current power system, is required to maintain close frequency regulation or load distribution control. To obtain higher precision, each of the prime movers is provided with calibrating or response-adjusting means.

In the case of prime mover 21, these responseadjus ing means are shown as comprising atento efiect a change in tension of the spring.

It will be apparent that an increase in spring. tension will tend to increase the speed at which governor 55 will maintain prime mover 21, while a decrease in tension will causethe prime mover to correspondingly lower its speed, the response characteristics of the governor being dependent upon the force which the flyball mechanism must overcome in effecting the closure of the input control valves.

To rotate gear wheel 67, a motor 69 is pro-' capable of reversible vided. This motor may be of any suitable type operation, and as shown,

1 it comprises an armature winding '10 and a-fleld winding made up of two separate oppositely wound sections r and l. Energization from a direct-current source of the armature through field winding 1 causes the motor to rotate in a by the voltage direction which tends to raise the speed and output of generating unit A, while energization of the motor through field winding 1' causes it to rotate in a-speedand load-lowering direction.

The prime movers of units B, C and D are similarly provided with governor calibrating means which include tension springs controlled by adjusting motors'I-i, '15 and '16, respectively. These means operate in a manner comparable to that just explained for biasing member and adjusting motor 69 of generating unit A.

To control the governor adjusting motors of the generating units any-s table means for selectively completing one or the other of two circuits, such as a frequency regulator '18 (Fig. 2) may be employed. Regulator "I8 is illustrated as being of a well known speed-responsive centrifugal-element step-by-step operation type. The frequency change-responsive element.80' is driven by a synchronous acting" in a main power circuit 34-35-36 to which the generating units are connected. n

Element 80 is provided'with flyball members 84 which are mechanically v cally movable member 85 in such manner that an increase in rotatlve speed of element ,80 causes member 85 to move upwardly, while a decrease in speed permits of a downward movement. These movements are transmitted to a contact-carrying arm 8'1 which is pivoted at one end ,88 and which carries at the other end contact members 90 and the manner shown. A 93 exerts a downward force on arm 8'1 91 spring-supported in weight to oppose the upwardly acting force of member time intervals.

- of which engagement power circuit voltage causes member 8'1 robe raised to a position in which contact member ,90 engages with the member 96' at regular time intervals. 4 Engagement of the pairs 01' regulator 85, while a dashpot damping to increase stability. I

In cooperative relation with the movable contact membersv 90 and 91 are disposed contact members 96 and 9.'1-which are carried by supporting arms 98 and 99,,each of'which is pivoted to the left-hand end in the manner shown. The

element 95 is utilized right-hand ends of these arms are caused, by means of tension 1 members 101 and 102, respectively. These camsprings, to bear against cam members are disposed to be continuously rotated,

- as by a motor 104, in such manner that the regulator contact members96 and 9'1 move towards and away from each other at regularly spaced In operation of the-regulator '18, normal irequency of the voltage acting inpower H circuit 34- 35-36 rotates the motor 82 at such speed that arm 87 is maintained at the intermediate elements 90 and 91 do not engage with elements 96 and 97. A decrease in frequency allows arm 8'1 to move downwardly to the position in which contact member 91 is caused to engage member 9'1 at regularlyspaced time intervals, the duration P riods varies with the dis= placement from the neutral position of arm 8'1. L kewise, an increase in the .fre'que'ncy o1 the contacts motor 82 which is energized linked with a vertior neutral position illust'ratedin which contact 1 90 -96 and 91-97, respectively, control the actuation of two load control relays L and R, which, when actuated to the closed contact position by energization of their operating windings, serve to energize one of the load-adjusting motors 69, '14, '15 or '16 associated with the generating units in the load-raising or load-lowering direction, respectively, in a manner to be further explained.

It will be apparent that regulators of types other than the frequency-responsive device '18 may also be utilized to control the actuation of load-control relays L and R, also that means for selectively assigning the relay control among a number of different regulators at the will of an hand position, shi1ts the relay-actuating circuits to a second regulator represented at 714, which regulator may be of'any one of a number of types well known in the art, such, for example, as a load regulator.

It will further be apparent that manuallyoperable push buttons may likewise be utilized to efiect the relay control, ,in which case the loadadjusting impulses which are routed through the program-load controller of our invention for selective assignment among the several generating units in the power system may be supplied by an operator. Such manual control means may comprise a pair of push buttons ML and MR which, when respectively depressed, effect the actuation of load-controlrelays L and R.

As connected, these pushbuttons are effective at all times irrespective of the position or regulator-selecting switch '100. However, when it is desired that the station load be adjusted manually, the blades of switch "100 may be moved to the open of theregulators '18.and"114 are disconnected from the load-"control relays. For such a condition, push buttons ML and MR comprise the only source or load-adjusting impulses so that manual control of station load maybe satisfactorily eflected.

Inthe explanation of the system of our invention which is to follow, it will be assumed that switch 100 is elosedto the left-hand position in which frequency'regulator "18 is connected with the load-control relay actuating windings. It fwill be appreciated, however, that, insofar as the operation of the program-load control system is concerned, the load-adjusting impulses can as well be supplied from the second regulator master-load-adjusting I position in which both 714, or manually through'the operation of the push buttons mentioned.

I In order to obtain improved operating eniciency of generating units desired that the load distribution among them be regulated in some predetermined manner, rather than being allowed to assumes pro rata division, such'as would result were the load-atl- 'justing motors of all ously subjected to load-changing impulses f the regulator '18. Thus, as the load demand upon the main power erators are directly connected changes, and tends to cause the frequency to differ from the desired value, instead of permitting the regulator toeflectchanlesintheoutputotallotthe A,B,Candl ),itis,

circuit to which the four gen-' the units to be simultanegenerators to restore the frequency, it is desired that theregulator control only one of the units, and, after the output of this unit has been adjusted to a predetermined value, that the regulator control be suitably transferred to another another of a plurality of generating units or other machines in accordance with a predeterof conductor terminals 111 communicating with shownin Figs. 1 and 0 conductors leading 17 are shown nected .with the in the manner shown.

' with receptacles Cp,

mined schedule, and is capable of efiecting the load distribution control requirement outlined above in a system in which the prime movers are of the single control valve type. Our invention is directed to a system employing multicontrol valve prime movers. Such a program control system is shown, in Figs. 1 and 2, as comprising a motor-driven selector switch 106 con-,

nected intermediate the generating units A, B, C and D and the load-control means of which regulator 78 is representative; 1

Intermediate the selector switch 106 and the generating units controlled are disposed prosequence' receptacles designated by S1 to S12, inclusive, and a similar number of machine receptacles, the sequence receptacles being conselector switch 106 of Fig. 2'

Each of the generating units A, B, C and D is provided .with a set of three machine receptacles, the three receptacles in each set respectively corresponding to the three inputcontrol valves of the prime mover. Thus, unit A is provided with receptacles Ap, As, and At associated with the primary, secondary and tertiary valves of turbine-21, respectively. Similarly, 'unit B is provided with receptacles Bp, Be, and Bt; unit C Cs and Ct, and unit D with receptacles Dp, Ds, and Dt. I v

The sequence and machine receptacles are intrconnected by means of removable jumper connecti'ons of any suitable type, one preferred form of which is illustrated in Fig. 17. In Fig. 17, S designates one of the stationary sequencereceptacle members which may comprise a block of insulating material 110 which carries a plurality contact-making clips-112 mounted in the insulating block. It w trol circuit conductors of the transfer system 2 are joined with terminals 111. In Fig. 17, M similarlydesignates one of the machine-receptacles which. may be of, a construction identical terminals being joined with the control circuit to the turbine of the generating unit. While the receptacle members of Fig.

ber called for by the system .of Figs. 13-14, it will be understood that only fourof these terminals will be used in'the system of Figs. 1-2.

To establish the removable Jumper connections, indicated in the system of Figs. 1 and 2 by the dotted lines, removable plug devices 114 and 115 are'provided for insertion into receptacle members S and. M. As shown, each device may comprise a block of insulating material 117 from which project 'a plurality of conducting material studs 118 which are disposed to fit snugly into the clip members 112 of the stationary receptacle when the plug assembly is inserted therein. Electerns involving be understood that the conto that just described, its

as having nine terminals, the num-' trical connections from studs 118 may be brought from the plug in the which cord terminates at its other end in the second plug member designated-in Fig. 17 as 115, which is provided with an equal number of contact studs symmetrically connected to those of the first mentioned plug. That is, the top studs of the two interconnected plugs are joined together, the second studs from the top of both similarly connected, etc. -The flexible cord 120 thus comprises a plurality of separately insulated conductors, the two ends of each of which termiform of a flexible cord 120,

nate in similarly positioned studs in the plug, 1

members.

The switching means just described are for program-selecting ser.vi e and, as has been mentioned, are disclosed and laimed in the previously mentioned Patent No. 1,920,544.

For purposes of preliminary explanation of the program-load-control system depicted in Figs. 1 and 2, let it be assumed that the electrical connections indicated tween the sequence and machine receptacles are established in the manner there shown, asbythe use of interconnecting program members, shown and described in connection with Fig. 17. When such connections are made, the particular program of transfer operations given by schedule a in the table of Fig. 6 will be followed.

In the table of Fig. 6, which sets forth nine different programs of regulator transfer for increasing load demand, the circle-enclosed numerals opposite each of the schedule-designating letters indicate the sequential ranges of output defined by the input-control-valve openings of generating units, A, B, C and D, which the regulator is caused to consecutively make effective as the combined load demand on all of the generating units progressively increased from a minimum to a maximum. It will beunderstood that load demand changes in the load decreasing direction cause the sequences outlined in Fig. 6 to reverse themselves.

pointed out in the copending applications men-.

tioned, be effected in any suitable manner by means responsive to the loading of each of the several generating units involved. In power sysmulti-valve prime movers, it is found essential to utilize for this purpose contactmaking mechanisms operated in accordance with the position of the prime mover input-control valves, rather than wattmetric contact-making means disposed in the output circuits of the generators, the latter method being wholly inadequate in a program-load control system for multi-valve turbines, since there is no definitely fixed relation between the output of the generator and the exact position of the prime moverinput control valves, particularly when the steam pressure and vacuum is subject evento small variations.

As has been mentioned, and will be made more evident, those undesirable loading ranges of the. turbines within which it is desired to prevent continuous operation are determined by the points of valve-opening, so that-it is necessary that the ing, the preferred manner of actual arrangement by the dotted lines drawn be- ,W

. d 1,984,187 in a practical system being shown by Figs. 'l-

to 12 inclusive, which .,will later be described. In the simplified representation of Fig. 1, a contact member is illustrated as being mounted on the movable member of each input control valve of each of the several prime. movers, and, in cooperative relation with this contact member, two stationary members are shown as being positioned so that theyv will be selectively engagedjby the first-named member as the valve is adjusted from the open to the closed position. Electrical connections are made from these contact members to the control circuits of transfer-operation eifecting means. i

Thus, in the case of generating unit A, contact members 125, 126 and 127 are shown as being mounted upon the movable elements of the primary, secondary and tertiary valves 48, 49 and 50, respectively. In cooperative relation withmember 125 is disposed stationary contact members 129 and 130. Stationary contact members .131 and 132 are similarly disposed with respect to movable member 126 of the secondary valve,

while members 133 and 134 are'positioned to be engaged-by contact member 127 of the tertiary valve. V I As shown, the positioning of the stationary members is such that when the valves are in the minimum load or closed position illustrated, the movable'contact members engage stationary members 129, 131, and 133, respectively, while when the valves successivelyapproach the opened positions, the movable contact members carried thereby engage stationary members 130, 132 and 134, respectively. As will be more completely explained, in the preferred form of, operative system mentioned, the points of equivalent contact engagement are adjustable in order that the valve positions at which the transfer operations will be initiated may be set most advantageously.

In a similar manner, primary, secondary, and

tertiary valves of each of generating units B, C and D are provided with contact members, which,

in the closed positions of the valves, engage sta tionary mefnbers suitably positioned in cooperative relation thereto, while in the open positions operates with an 75 of the valves, 9. second set of stationary members is similarly engaged. In the diagram of Fig; 1,

the showing of these valve-actuated contacts is the same for all units, so that the detailed description which ,has been made in connection with unit 'A'is deemed sufllcient for the remaining three units. s

- The motor-driven selector switch 106 is shown as comprising four parallel-operated contactestablishing devices which include conductingmaterial strips Ll, R1, 8101, and F1, respectively.

Mounted in a row parallel to each conductor stripare a plurality of stationary contact points hich are disposed to be selectively connected with the strip by means of a movable contact-making brush device provided with two separate, but electrically connected, engaging surfaces, one of which bears upon the strip and' the other of which bears upon the contact. points. These brush devices which are designated at 136, 137, 138 and 139 inthe switch 106 of Fig. 2 are all carried by a bar of insulating material 141 which is mounted'in a manner to permit movement along the length of the conductor strips and the associated rows of stationary contact points.

Movement of brush-carrying bar 141 is effected by rotation 01 a threaded shaft 143 which cointeriorly threaded bushing 144 carried by the bar. The shaft carries a gear wheel 145 which is to be rotated by a switch-operating motor 146.

One preferred form of mechanical construction for selector switch 106 is illustrated in Figs. 15 and 16. In Fig. 15, which is a plan view of the switch, a base 500 ofv insulating material carries the plurality of conducting-material strips 502, alongside each of which contact points 504. The threaded 'shaft 143 is mounted in suitable bearings 506 and arranged to be driven through gearing 145 by the operating motor 146.

The insulating-material bar 141, which carries the, contact-making brush devices, is suitably attached to the interiorly threaded bushing 144, which transmits to the bar movements along the length of the conductor strips 502effected by rotation of shaft 143.

Each of the bruslidevices comprises two separate engaging fingers 510, one of which bears upon the conductor strip and associated row of contact points Supporting is mounted the rows of Y the other upon the projecting pin 513 and maintained in contact with g member 511 by means of a compression spring 515 held in place by a cotter-pin-secured washer 516. 1

When thus arranged, each of the contact fingers 510 tends to bear downwardly upon the con ducting surfafce below with a pressure which is independently maintained by the compression spring so. that unevenness in either the conductor strip or the contact points will be compensated for. Connection with the conductor strips and contact points is made to the securing bolts 51 which project through the insulating-material base 500. v

The usual limit switches 203 and 266 are provided for interruption of the motor circuit when the limit of switch moyementin the forward and backward directions, respectively, is reached. As illustrated, these limit switches are carried by a strip of insulating material 519 in such a manner that an upwardly projecting member. 520 will act to open the contact members thereof if the normal travel limits of brush-carrying bar 141 are exceeded.

To ensure proper parallel advancement of all of the contact-making brushes, an auxiliary guide rod 522 is provided to engage with abushing 523 carried by the movable bar member 141 and disposed to slide along rod 522'in a manner to steady the movement thereof.

lective connection with each of the conductor strips of the selector switch is determined by the maximum number of transfer operations which it is required that the program load control system effect when the total load demand on all .of'the generating units controlled changes from minimum to maximum, or to full capacity on all the machines. In the system of Figs. 1 and 2, it is desired that each of the four generating units have three distinct operating or load ranges,

determined respectively by the openlngof the primary, secondary and tertiary valves, which ranges are designated by the curves of Fig. 3.

twelve different active positions, one for each The number of contact points provided for sei Hence, the transfer. switch 106 should have I 

